Carrier-current multiplex signaling system



Dec. 15 1925. 1,565,522

J. S. STONE CARRIER CURRENT MULTIPLEX SIGNALING sis'rnu Filed Nov. 25, 1923 3 Sheets-Sheet a I INVENTOR 4 pi y Jake ,5

I ATTORNEY J. S. STONE CARRIER CURRENT MULTIPLEX SIGNALING SYSTEM Filed Nov. 23, 1923 3 Sheets-Shed. 5

IN VEN TOR By uZ/w aZmeJm I A TTORNEY i atented Dec. 15, @925.

UNITED STATES PATENT OFFICE.

JOI-IN STONE STONE, OF SAN DIEGO, CALIFORNIA, ASSIG-NOR 'IO AMERICAN TELE- PHONE AND TELEGRAFH COMPANY, A CORPORATION OF NEW YORK.

CARRIER-CURRENT MULTIPLEX SIGNALING SYSTEM.

Application filed November 23, 1923. Serial No. 676,624.

To all whom it may concern Be itlrnown that 1, JOHN STONE SiroNn, residing at San Diego, in the county of San Diego and State of California, have invented certain Improvements in Carrier-Current hiultiplex Signaling Systems, of which the following is a specification.

An object of my invention is to provide an improved method and apparatus for selective reception of currents of various frequencies in a multiplex receiving system. Another object of my invention is specifically to guard each of several branch re ceiving circuits in a multiplex system from effects due to currents appropriate to the other branches. By the practice of my invention it is made possible to put the channels closer together along the frequency range in a multiplex carrier current system, so that more message channels can be pro vided within a given range of carrier frequencies without increasing the inherent selectivity of the individual receiving branches. These objects are attained by establishing certain associative relations between the branches of which examples will be shown in the following specification. In this specification certain embodiments of the invention are disclosed with the understanding that these are illustrative examples and that the invention is defined in the appended claims.

Referring to the drawings, Figure 1 is a diagram illustrating one embodiment of my invention. Figs. 2 and 3 are curve diagrams to which reference will be made in explaining the operation of the apparatus of Fig. 1. Fig. 4 is a diagram showing a modification as compared with Fig. 1. Figs. 5 and 6 are curved diagrams to which reference will be made in explaining the operation of the apparatus of Fig. A. Fig. 7 shows still another modification as compared with Fig. 1. Fig. 8 is a simplified diagram showing the principle involved in extending the invention'to a larger number of receiving branches; and

Fig. 9 is a curve diagram to which refer-. ence Wlll be madein discussing the princi ple of the invention.

Referring to Fig. 1, Z7 is a transmission line over which are sent alternating currents of several different frequencies which are intended to be received in respective branches such as 1, 1 and 2, 2. The branch 1, 1 comprises in series a condenser C and an inductance L Across the condenser G there is connected the input of an audion relay R whose output goes to the demodulator D with the associated telephone rec'eiver'T Another audion relay R is connected in a similar manner across the c011 denser C and its output goes through a phase shifter 0 and thence to the terminals of the demodulator D 7 Associated with the inductance L by means of a one-to-one transformer M are an audion relay R demodulator D and telephone receiver T corresponding respectively to R D and T Associated with the inductance L 'by means of a one-to-one transformer M are the audion relay R and phase shifter designated corresponding respectively to R and and the output from the last mentioned phase shifter goes to the demodulator D The elements of apparatus mentioned in the. foregolng explanation have predeter-' mined values for their electromagnetic constants that will be mentioned in the follow-.

ing explanation'of the mode of operation. It is assumed that the current coming in over the line ZZ consists of two superposed alternating currents of respective frequen cies f and to which respectively the branches 1, 1 and 2, 2 are resonant.

Each

branch has a certain selectivity S defined by the equation L dere Where the resistance R of the branch, and its inductance L and capacity C are so related that S is the same for both branches although f and are ditterent.

The potential difi erence across the other Now let the audion relay R be adjusted so that the ratio of its amplification (a to that of the relay R ((1 shall be given by the expression x i flfz Also, let the phase shifter 6 be adjusted so E f s This is the electromotive force derived from the branch 2, 2 and applied to the terminals of the demodulator D To get the resultant electroinotive force on the demodulator In practical cases the ratio f /f Will not differ much from unity, so that Without sub- The impressed electromotive force on the terminals of each branch is given by the expression E cos 2 f 2+E cos 2 7 t (2) and accordingly the potential ditierence across the condenser Q will be condenser C is that its output Will be retarded relatively to the output of amplifier R by the time interval 1 22:1?) tan S Making these changes in relation to equation 4, the result is as follows:

D multiply the right hand side of equation 3 by 1 and subtract equation 7, and the result is sin {Zn-f t+ 1 tan (S) stantial error We can assume that this ratio 1s unity in equation S, which then reduces to fifz tude of the potential difference at the terminals of the demodulator D is determined solely by the amplitude of the incoming signal train of frequency f The result has been secured that the demodulator D responds in amplitude only to the current of frequency 7' and is not attested by the other current of frequency Vihthout going into details, it can be shown in a similar manner that 1f the ratio of the amplification of relay R to that of relay R be given by the expression 0) 2 f.,1 f22}2 l 1]? and if the phase shifter designated -6 introduces the time lag given by theexpresthe incoming alternating current of frequency f Referring to Fig. 9. in which the abscissas are frequencies the two curves show the overlapping resonance curves for the two frequencies f, and f As shown in 2, the amplitude of the component of the interfering frequency in each branch is aboutv 10% of the amplitude of the component proper to that branch. The vertical dotted lines in Fig. 2 indicate two bands of frequencies of the same width and having re spective mean frequencies f, and f \Ve may properly assume that the impressed electromotive force across each branchcircuit l, 1 0r 2, 2 presents a continuous fre quency spectrum of uniform intensity throughout the respective band of the width shown in Fig. 2. The frequency spectrum of the potential difference developed by the relay R at the terminals of the demodulator D is illustrated by the line a-b-c-cZ-e-f-g-h-ij-w of Fig. 3. The frequency spectrum of the potential difference developed by the relay R at the terminals of the same demodulator D is illustrated by the line a-blc-Z-f-gm-n-0-j-w of Fig. 3, and accordingly the frequency spectrum of the resultant potential difference at the terminals of the demodulator D is given by the line a-b-c-pe- -g-r-j-w of Fig. Thus it will be seen that the response due to frequency f, is substantially annulled.

Fig. 4: corresponds with Fig. 1 except that respective band filters BF and BF are employed in connection with the demodulators. lViththis explanation, Fig. 4; will readily be understood by comparison with Fig. 1. Correspondingrespectively to the diagrams in Figs. 2 and 3 for the apparatus of Fig. 1, we have the diagrams of Figs. 5 and 6 for the apparatus of Fig. 4.

Fig. 7 illustrates another form of the invention in which the potential differences across the condensers and coils are first impressed upon the demodulators D D D and D and then upon the relays R R,, R, and R In this form of the invention it is no longer necessary to use the phase regulators designated 9 and 6 in Fig. 1,

and moreover the potential amplifying functions of the relays R R R and B, may be performed by transformers or even by the demodulators D D D and D When there are more than two receiving branches, the application of the principle of the invention is suggested by the pairs of branch conductors coming in from the right as shown in Figs. 1, 4 and 7. Referring particularly to Fig. 1, the upper pair of conductors coming in from the right bring the proper corrective electromotive force to the terminals ofthe demodulator D to annul the direct effect of the frequency in the line ZZ appropriate to the branch Not only must such conductors come in from the branch 33, but they must go from the branches 1, 1 and 2, 2 to the branch 3, 3. A complete system showing these intercone nections in highly diagrammatic form is illustrated in Fig.

Referringto Fig. 9, the curve A represents the resonance curve of the branch circuit to which the frequency f, is appro But this is not the curve-for the priate. terminals of the associated receiver T because it receives certain annulling electromotive forces from all the other branches, and the resultant curve at the terminals of the receiver T is given by the curve B. This has its peak at the frequency f,, but it has dimples at all the other frequencies of which only two are shown in the diagram, so that at all the other frequencies the resultant is null, and at these other frequencies the telephone T gives no response.

It will be seen that with a certain degree of selectivity in each of a plurality of receiving branches appropriate to respective frequencies, by my invention the direct effect of the frequencies in one branch is counteracted by cross-connections to the remaining branches. Each receiving branch is. made peculiarly and specially non-responsive to the other frequencies of the system. In this way, without resorting to any measures to increase, the selectivity of each branch, the frequency channels can be crowded closer together and more message channels can be provided Within the available frequency range for the system under consideration. It is this one-way association feature which prevents reactions of the various circuits upon one another that makes the object of this invention attainable. Oircuits s'o related I call associated circuits in counter-distinction to coupled circuits. The object of this invention can not be accomplished by coupling the various circuits but only by the-one-way associations described or their equivalents.

I claim:

. 1. A conductor carrying currents of several different frequencies to be separated in their eifects, respective branch conductors appropriate to the respective frequencies,

respective apparatus to beactuated by electromotive forces in said branches and crossconnectingmeans to each apparatus from the other branches to neutralize the effect through the corresponding branch due to currents to which the other branches are appropriate.

2. The method of discriminating among the different frequencies in a multiplex carrier current receiving system which consists in annulling in each branch the frequencies received therein appropriate to the other branches by means of currents in proper amplitude and phase relation derived from those other branches.

3. A conductor carrying currents of several different frequencies to be separated in their effects, respective branch conductors appropriate to the respective frequencies, respective apparatus to be actuated by electromotive forces in said branches and unilateral conducting means connecting each apparatus with the other branches to neutralizethe effect through the corresponding branch due to currents to which the other branches are appropriate.

4. A conductor carrying currents of several different frequencies to be separated in their effects, respective branch conductors appropriate to the respective frequencies, respective apparatus to be actuated by electromotive forces in said branches and crossconnecting means to each apparatus from the other branches to neutralize the effect through the corresponding branch due to currents to which the other branches are appropriate, each such cross connection comprising an adjustable amplifier and an adjustable phase shifter.

5. A conductor carrying currents of several different frequencies to be separated in their effects, respective branch conductors appropriate to the respective frequencies, respective apparatus to be actuated by electromotive forces in said branches and associated circuit connections to each apparatus from the other branches to neutralize the effect through the corresponding branch due to currents to which the other branches are appropriate.

6. The method of discriminating among the different frequencies in a multiplex carrier current receiving system Which consists in annulling in each branch the frequencies received therein appropriate to the other branches by means of currents in proper amplitude and phase relation derived through associated circuit connections.

In testimony whereof, I have signed my name to this specification this 14th day of November, 1923.

JOHN STONE STONE. 

